The reproduction of a wing having a profile structure with a high aerodynamic potential has been the subject of a great deal of research. As a wing for the propulsion of a craft is meant to be used whatever the direction of the apparent wind, the main challenge is to precisely reproduce profiles with a high aerodynamic potential in a symmetrical way.
Thus, systems have been developed which use flexible external envelopes, with or without extension. The external envelope is thus reproduced by means of one or more flexible elements, mostly in the form of battens, these battens being deformed by internal or external mechanisms.
Certain known devices, described in particular in documents U.S. Pat. No. 6,863,008 and WO8600591, use a symmetrical front element whose end corresponds to the leading edge of the profile, which in fact entails two limitations. On the one hand, the profile obtained then has an axis of symmetry on the leading edge and cannot reproduce with precision the known optimized profiles having a high curvature such as S1223 or FX74CL5 MOD which do not possess this symmetry. On the other hand, these systems can then reproduce, with an external envelope that is continuous and can be only very slightly extended, only profiles for which the differences in length between the intrados and the extrados are negligible, i.e. which have a low curvature and do not correspond to known optimized profiles such as S1223 or FX74CL5 MOD.
Other known devices, described in particular in documents U.S. Pat. No. 4,895,091 or 4,386,574, succeed in increasing the curvature of the assembly by separating the back of the envelope, thus creating a discontinuity of the external envelope at the rear part of the profile, which will weaken the whole device, limit the precision of the control of the rear shape of the profile and create aerodynamic perturbations at the rear part of the profile in comparison with known optimized profiles such as S1223 or FX74CL5 MOD.
The devices described in particular in documents U.S. Pat. No. 3,332,383 or 6,045,096 are able to cause a part of the external envelope to slide on a part of the internal structure, the shape of said internal structure being meant to reproduce the shape of an aerodynamic profile, generating thereby frictions which weaken the assembly and limit the control precision.
In addition, the devices described in particular in documents U.S. Pat. No. 4,624,203 or 4,341,176 use a mechanical internal structure in which some parts slide against each other in order to reproduce the shape of an aerodynamic profile, generating thereby frictions which weaken the assembly and limit the control precision.
The devices described in particular in documents U.S. Pat. No. 5,181,678 or 7,384,016 are based on the use of a flexible internal structure in order to reproduce the shape of an aerodynamic profile, resulting in an overall fragility of the internal structure and a limitation of the precision of the assembly.
Double-wheeled sail devices are also known, as described in GB2085387, which makes it possible to increase the length of one side of the envelope in order to create a difference in length between the extrados and the intrados while keeping the tail integral with the envelope. The system described in document DE4207539 uses an assembly composed of a symmetrical front part and two battens for forming a closed assembly having a difference in length between the extrados and the intrados.
However, the external envelope is not formed by a single flexible element, and this can weaken the device. Moreover, the symmetrical front part induces symmetry in the curvature, which does not make it possible to precisely reproduce the curvature variation of optimized profiles such as S1223 or FX74CL5MOD. The control structure is not defined on the whole profile and there is no additional control of the local curvature on the battens. It should also be noted that the intrados has no concavity and that the device uses a sliding connection between the structure connected to the mast and the battens, which creates frictions and weakens the assembly.
Thus, none of the known profile structures can reproduce with precision and robustness known optimized profiles such as S1223 or FX74CL5 MOD by optimally controlling a single flexible, continuous external element, which can be only very slightly extended. This explains in part why, in the present state of the art, competition yachts, such as AC72 or AC45, preferentially use an assembly of rigid symmetrical profiles hinged to one another, these various profiles acting directly as a skin external to the assembly. In this case, it is possible to reproduce high curvatures on the entire wing. However, the external shape then has curvature discontinuities, which increases the shape drag of the assembly.